* {
    margin: 0px;
    padding: 0px;
}

/**/
a {
    text_decoration: none;
}

.box_header {
    width: 100%; /*宽度*/
    height: 100px; /*高度*/
    background: #333; /*背景色*/
}

.box_top {
    width: 500px;
    margin: 0px auto;
    background: indianred;
}